A two-port solenoid valve of a type in which a valve member for opening/closing a flow passage by approaching/separating from a valve seat in the flow passage connecting two ports is opened/closed and operated by a movable iron core of an electromagnetic operation portion in a direct-driven manner is publicly known as described in Japanese Unexamined Patent Application Publication No. 3-92687, for example.
This type of two-port solenoid valve usually has a fixed iron core and a movable iron core attracted to each other by a magnetic force generated by electricity flown through an excitation coil, a valve member held by the movable iron core, and an iron-core return spring for biasing the movable iron core toward an initial position away from the fixed iron core. And the two-port solenoid valve is configured such that when the excitation coil is not electrified, the movable iron core is separated from the fixed iron core by an biasing force of the iron-core return spring, the valve member held by the movable iron core is pressed onto the valve seat and the flow passage is closed, and when the excitation coil is electrified, the movable iron core is attracted to the fixed iron core so that the valve member is separated from the valve seat and the flow passage is opened.
Here, while the excitation coil is being electrified, the movable iron core is attracted to the fixed iron core so that the iron-core return spring is compressed. Thus, if electricity to the excitation coil is cut off from this state to be switched to a valve-closed state, the movable iron core is separated from the fixed iron core with great force by the biasing force of the iron-core return spring, the valve member collides with the valve seat with a large impact force by an inertia force of the movable iron core, and repetition thereof makes the valve member abraded easily.
Therefore, in the solenoid valve described in the above Patent Document, a buffer spring is interposed between the valve member and the movable iron core so that the impact force is absorbed by the buffer spring.
However, since in the above conventional solenoid valve, a cavity is formed on a front end face of the movable iron core in which the valve member is housed, the movable iron core should be formed in a special shape provided with a cavity of the size and shape according to the valve member, which makes configuration complicated and manufacturing troublesome. Also, when the valve seat should be provided at a position far from the movable iron core for design convenience, the length of the movable iron core can not be prolonged for that portion in many cases, which can not be easily coped with.